Back to EveryPatent.com
United States Patent |
5,230,316
|
Ichihara
,   et al.
|
July 27, 1993
|
Method and apparatus for detecting knock in an internal combustion engine
Abstract
A method and apparatus of detecting knocking in an internal combustion
engine having a crankshaft uses a knock detecting sensor to detect
vibration caused by knocking. The signals from the knock detecting sensor
are detected between a first and a second moment of time (i.e. a
measurement window) and at least one of the first and second moments of
time are independently varied in dependence upon a vibration spectrum of
frequencies to be detected. In a preferred embodiment a plurality of
frequency spectra, each having a different first and second moment of
time, are each separately analyzed for determining knock intensity. The
moments of time are represented by first and second angles of the
crankshaft. A plurality of measurement windows are advantageously used to
determine the level of knocking and if the level exceeds a predetermined
level the ignition timing for the engine is retarded. The frequency of
maximum amplitude is arranged in operation to be the center frequency of a
frequency spectrum determined by the measurement window.
Inventors:
|
Ichihara; Takanobu (Katsuta, JP);
Katogi; Kozo (Hitachi, JP);
Tokuda; Hiroatsu (Katsuta, JP)
|
Assignee:
|
Hitachi, Ltd. (Tokyo, JP)
|
Appl. No.:
|
690851 |
Filed:
|
April 24, 1991 |
Foreign Application Priority Data
| Apr 27, 1990[JP] | 2-110291 |
| Jul 06, 1990[JP] | 2-177422 |
Current U.S. Class: |
123/406.38; 73/35.09 |
Intern'l Class: |
F02P 005/14 |
Field of Search: |
123/425,479,435
364/431.05
73/35
|
References Cited
U.S. Patent Documents
4466406 | Aug., 1984 | Hartung | 123/425.
|
5005549 | Apr., 1991 | Pannpaindras et al. | 123/479.
|
5012782 | May., 1991 | Tokuda | 123/425.
|
5040510 | Aug., 1991 | Krabs et al. | 123/425.
|
5083278 | Jan., 1992 | Matsuura | 364/431.
|
5088044 | Feb., 1992 | Matsuura | 364/431.
|
Foreign Patent Documents |
2571141 | Apr., 1986 | FR | 123/425.
|
Other References
Patents Abstracts of Japan, vol. 7, No. 117 (P-198)(1262) May 21, 1983 and
JP-A-58 037 531 (matsushita) Mar. 4, 1983.
Patents Abstracts of Japan, vol. 8, No. 183 (P-296)(1620) Aug. 23, 1984 and
JP-A-59 073 750 (Matsushita) Apr. 26, 1984.
|
Primary Examiner: Nelli; Raymond A.
Attorney, Agent or Firm: Ladas & Parry
Claims
We claim:
1. A method of detecting knocking in an internal combustion engine having a
crankshaft and a knock detecting sensor including the steps of
determining in terms of first and second angles of crankshaft angle at
least one spectrum of frequencies where engine vibration occurs due to
knocking,
detecting engine vibration signals caused by knocking with said knock
detecting sensor between said first and second angles of said crankshaft,
actively independently varying at least one of the first and second angles
to track said vibration spectrum of frequencies to be evaluated, and
calculating the knock intensity by determining if the level of said
detected vibration signals exceed a predetermined level for use in
controlling engine ignition timing.
2. A method as claimed in claim 1 wherein a plurality of frequency spectra
each having a different first and second moments of time are separately
analysed for determining knock intensity.
3. A method as claimed in claim 1 wherein said plurality of frequency
spectra each have different centre frequencies and said crank angles are
varied to maintain the centre frequencies within the first and second
angles.
4. A method as claimed in claim 3 wherein the first crank angle is variable
and the difference between the first and second crank angles is
predeterminedly fixed.
5. A method as claimed in claims 3 wherein the crank angle range between
the first and second crank angles is limited to reduce the effect of
vibration caused by mechanical noise, such as by reciprocating engine
inlet and exhaust valves.
6. A method as claimed in claim 3 wherein when the intensity of knocking
exceeds said predetermined level then ignition timing of said engine is
retarded.
7. A method as claimed in claim 1 wherein the spectrum of frequencies is
detected at a plurality of sampling points within said spectrum wherein
the samples at said sampling points are analysed.
8. A method as claimed in claim 7 wherein said analysis is Fast Fourier
Transform or Walsh to Fourier Transform analysis known per se.
9. A method as claimed in claim 1 wherein said first and second angles are
varied in dependence upon engine r.p.m., engine water temperature, intake
air temperature, intake air humidity or engine mileage.
10. A method as claimed in claim 3 wherein said spectra of frequencies is
each representative of a mode of vibration within a respective cylinder of
said engine.
11. A method as claimed in claim 7 wherein for each frequency spectrum, the
frequency of maximum amplitude is detected by analysing data at two or
more consecutive frequency samples.
12. A method as claimed in claim 11 wherein said frequency of maximum
amplitude is multiplied by a weighting factor and the weighted frequency
of maximum amplitude for each mode are summed to provide a tone index
whereby knock is detected by comparing said tone index with a
predetermined signal.
13. A method as claimed in claim 11 wherein if said frequency of maximum
amplitude is not centrally located within said frequency spectrum the
first and second crank angles are shifted in a next cycle to centralise
said frequency of maximum amplitude.
14. An apparatus for detecting knock in an internal combustion engine
comprising a crankshaft angular position detector, a knock detecting
sensor for detecting engine vibration caused by knocking, a timing means
connected to said position detector and said knock detecting sensor for
evaluating signals from said knock detecting sensor between a first and a
second crankshaft angular position, and means for actively independently
varying at least one of the first and second angles to track a vibration
spectrum of frequencies detected by said knock detecting sensor whereby
said spectrum of frequencies is maintained between said first and second
crankshaft angular positions.
15. An apparatus as claimed in claim 14 further including means for
evaluating said vibration spectrum of frequencies detected and means for
comparing an output of said evaluating means with a means producing a
predetermined signal level, and means for varying the ignition timing of
said engine signal if the output of the evaluating means exceeds said
predetermined signal level.
16. A method of detecting knocking in an internal combustion engine having
a crankshaft and a knock detecting sensor, said method comprising the
steps of:
predetermining a plurality of crank angles at which evaluation of output
signals from said knock detecting sensor is started and a plurality of
ranges of crank angel in which said evaluation of output signals is
carried out for respective ones of a plurality of different predetermined
detection frequencies;
varying said plurality of different predetermined detection frequencies to
thereby change said crank angle and said crank angle range in dependence
upon a vibration spectrum of said plurality of different predetermined
frequencies so that said crank angle range in which said vibration
spectrum is more than a predetermined level is relatively narrow;
setting, in an engine control unit, one of said plurality of crank angles
and one of said plurality of crank angle ranges which is relatively
narrow, respectively, and
detecting engine vibration caused by knocking with said knock detecting
sensor in said set crank angle range from said set crank angle.
17. A method of detecting knocking in an internal combustion engine
according to claim 16, wherein said set crank angle and said set crank
angle range are limited to reduce noise vibrations.
18. A method of detecting knocking in an internal combustion engine
according to claim 16, wherein said detection frequencies are changed
according to the number of revolutions of the engine and said set crank
angle and said set crank angle range are changed according to the varied
detection frequencies.
19. A method of detecting knock in an internal combustion engine having a
crankshaft and a knock detector sensor, including the steps of
predeterminedly locating a plurality of frequency spectra where knocking is
expected,
converting each said location to an angle of rotation of said crankshaft to
thereby define windows of said crank angular rotation where said spectra
are expected,
detecting knock signals with said sensor,
determining the detected knock signals above a predetermined amplitude,
actively shifting the start of each said window in dependence upon the
knock signals above said predetermined amplitude to maintain the detected
knock signals above said predetermined amplitude within said window, and
evaluating the intensity of knocking from said spectra of knock signals for
providing a control signal to change an ignition timing of said engine.
20. A method as claimed in claim 19 wherein said window may be altered in
length to reduce the effect of vibration caused by mechanical noise such
as reciprocating engine inlet and exhaust valves.
21. A method as claimed in claim 19 wherein each said window is altered in
at least one of position and length to maintain the maximum frequency
associated with said window approximately centrally in said window.
22. An apparatus for detecting knock in an internal combustion engine
comprising a crankshaft angular position detector, a knock detecting
sensor for detecting engine vibration caused by knocking, timing means
connected to said position detector and said knock detecting sensor for
evaluating signals from said knock detecting sensor above a predetermined
level between a first and a second crankshaft angular position, means for
actively varying at least one of the first and second angles of crankshaft
to track a vibration spectrum of frequencies detected by said knock
detecting sensor to be above said predetermined level, means for
maintaining a maximum frequency within said spectrum of frequencies within
said first and second crankshaft angular positions, and means for varying
the ignition timing of said engine in dependence upon the knocking signals
being above said predetermined level.
23. An apparatus as claimed in claim 22 wherein a plurality of timing means
are provided for evaluating signals from said knock detecting sensor each
between respective first and second crankshaft angular positions, said
crankshaft angular positions being representative of frequency spectra
where knocking is expected.
24. An apparatus as claimed in claim 22 wherein said maintaining means
maintains said maximum frequency approximately centrally between said
crankshaft first and second angular positions.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of detecting knocking in an internal
combustion engine and an apparatus therefor.
2. Description of Related Art
There are various kinds of known knock detecting methods and apparatus
therefor adapted to detect a knocking phenomenon occurring in an internal
combustion engine. For example, Japanese Patent Laid-open No. 45520/1983
discloses a knock detecting apparatus adapted to filter a frequency, which
is peculiar to knocking, of an output signal from a knock detecting
sensor, and to decide the occurrence of knocking by judging whether the
amplitude of the frequency component exceeds a predetermined level or not.
However, in this prior art apparatus, a knock signal is always evaluated in
the same range of crank angles, that is a predetermined "window" position
and arcuate length of crank angles is used for the knock detection.
Because the range over which knock detection is made is predeterminedly
fixed, it is not possible to accurately determine the crank angle at which
the maximum amplitude of knocking occurs. In this respect, the maximum
amplitude of knocking varies with frequency and the present inventors have
found that the frequency varies with crank angle position. If, as in the
prior art, an overly wide window is used to detect the frequency of
knocking, the window position also being fixed, so it has been found that
noise frequency components based, for example, caused by the vibration of
a valve, can have a major effect in the measurement window and cause a
misjudgment of the frequency (and thus crank angle) of knocking.
It will be appreciated that the engine block has a particular resonance
frequency and that the frequency of knocking in the prior art is detected
by evaluating the energy of the vibration. As mentioned above, vibration
from mechanical sources made by the operation of, for example, inlet and
exhaust valves, cause other resonant frequencies. It is disclosed in
Japanese Patent Application Laid-Open No. 63-219874 to use more than one
filter to separate particular resonance frequencies. More than one filter
is normally used if analog comprised of discrete parts are used or if
digital filters are used.
However, both the above-mentioned prior art attempts to accurately detect
the frequency and, hence, crank angle position of knocking are inflexible,
and because filters are used it is essential that the central frequencies
of the filters are predeterminedly fixed. This makes it impossible to
correctly adjust the filters central frequencies to resonance frequencies
in a situation where resonant frequencies change due to a change in the
operating conditions of the engine and the aged deterioration of the
engine itself. Thus, the prior art is unable to implement a high precision
detection of knock in internal combustion engines. Moreover, the prior art
attempt has the disadvantage that if analog filters are used, a like
number of filters are required as the number of frequencies to be
separated, thereby increasing the cost and size of the filters.
It is an object of the present invention to attain an improvement in knock
detecting accuracy, which cannot be completely effected by the above known
techniques, on the basis of the discoveries made by the inventors of the
present invention in their various experiments concerning the relationship
between the frequency of a detected knocking signal and a crank angle, and
to provide a knock detecting method and apparatus, which are capable of
improving an internal combustion engine output power and fuel consumption.
SUMMARY OF THE INVENTION
According to a first aspect of this invention there is provided a method of
detecting knocking in an internal combustion engine having a crankshaft
and a knock detecting sensor including the steps of detecting engine
vibration caused by knocking with said knock detecting sensor between a
first and a second moment of time and independently varying at least one
of the first and second moments of time in dependence upon a vibration
spectrum of frequencies to be detected.
Thus, in the broadest aspect of the invention the "window" at which
detection occurs has the start location thereof movable in time and the
period of the window of detection is variable in dependence upon time, the
essence being that the window is as narrow as possible and movable to
detect the maximum frequency of vibration.
Because the phenomenon of knocking occurs over a frequency spectrum it is
desired that a plurality of frequency spectra each having a different
first and second moment of time are each separately analysed for
determining knock intensity.
It will be appreciated that the first and second moments of time may be
represented by first and second angles of the crankshaft, although it is
to be understood that it is not strictly necessary to relate the moments
of time to crankshaft angles, such being performed for convenience.
Advantageously, a plurality of frequency spectra are detected each having
different center frequencies.
As described above, the start position of the window is variable in
position and so the first crank angle is variable but, in some
circumstances, it may be preferred to make the window length
predeterminedly fixed and so the difference between the first and second
crank angles may be predeterminedly fixed. It is to be noted, however,
that the arcuate distance between the first and second crank angles is
smaller than in the prior art because the windows of this invention, over
which measurement is made, are movable in position, whereas in the filters
of the prior art, the window position and length were predeterminedly
fixed and necessarily had to be wide in order to detect the knocking
phenomenon. Thus, advantageously, the crank angle range between the first
and second crank angles is limited to reduce the effect of vibration
caused by mechanical noise, such as by reciprocating engine inlet and
exhaust valves.
Preferably, frequency spectra are analysed to determine an overall knocking
signal level and if said level exceeds a predetermined level then ignition
timing of said engine is retarded.
In a currently preferred embodiment the spectrum of frequencies is detected
at a plurality of sampling points within said spectrum wherein the samples
at said sampling points are analysed. In such an embodiment said analysis
is Fast Fourier Transform or Walsh to Fourier Transform, both analysis
known per se.
Because engine knocking varies in dependence upon engine operating
parameters, preferably sad first and second angles are varied in
dependence upon engine r.p.m., engine water temperature, intake air
temperature, intake air humidity or engine mileage.
Advantageously, said spectra of frequencies is each representative of a
mode of vibration within a respective cylinder of said engine. In an
embodiment of the invention, advantageously for each frequency spectrum,
the frequency of maximum amplitude is detected by analysing data at two or
more consecutive frequency samples.
So as to improve the accuracy of the detection of knocking, said frequency
of maximum amplitude is multiplied by a weighting factor and the weighted
frequency of maximum amplitude for each mode are summed to provide a tone
index whereby knock is detected by comparing said tone index with a
predetermined signal. The weighting factor employed normally decreases
with the signal-to-noise ratio, that is the signal being the frequency of
knocking as against the noise being the internal mechanical noise of the
engine made by inlet valves, etc.
Thus, if the tone index is above the predetermined signal the engine
ignition is retarded.
Advantageously, if said frequency of maximum amplitude is not centrally
located within said frequency spectrum the first and second crank angles
are shifted in a next cycle to centralise said frequency of maximum
amplitude.
According to another aspect of this invention there is provided an
apparatus for detecting knock in an internal combustion engine comprising
a knock detecting sensor for detecting engine vibration caused by
knocking, a timing means for evaluating signals from said knock detecting
sensor between a first and a second moment of time, and means for
independently varying at least one of the first and second moments of time
in dependence upon a vibration spectrum of frequencies to be detected.
Preferably the first and second moments of time are represented by first
and second angles of a crankshaft of said engine.
In a preferred embodiment the apparatus includes means for evaluating said
vibration spectrum of frequencies detected and means for comparing an
output of said evaluating means with a means producing a predetermined
signal level, and means for varying the ignition timing of said engine
signal if the output of the evaluating means exceeds said predetermined
level.
Thus, by the present invention the window of frequency measurement may be
varied in position and in length and the centre frequency of the window
may be shifted in operation. By the use of this invention the detection of
knock is optimized and the result may be used to correct the ignition
timing of the internal combustion engine.
The apparatus of this invention conveniently has a knock sensor with a flat
frequency characteristic for operating over a range wide enough to include
knock detecting signals and, thus, to include more than one particular
frequency created on the occurrence of knock and is capable of detecting a
plurality of knock signals.
The aged deterioration of the engine is conveniently measured by detecting
the mileage of the automobile and the knock detecting apparatus of this
invention is capable of evaluating the deterioration of the engine and of
shifting the knock detecting measurement window in dependence upon aged
deterioration of the engine, whereby detection of knock is optimized. A
microcomputer is normally used to analyse the result of sampling so that
knock detection is evaluated in real time so as to optimize engine output
and combustion efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) and 1(b) show a waveform diagram and a graph respectively of the
relationship, which constitutes the basis of the present invention,
between the range of crank angles after top dead center (ATDC) in which an
output signal from the knocking sensor is picked up (detected) and a
vibration component;
FIGS. 2(a)-2(f) show in graphical form a method of determining an optimum
range of crank angles corresponding to frequencies to be detected;
FIG. 3 shows the entire system of a control apparatus for an internal
combustion engine which employs an embodiment of the knock detecting
apparatus in accordance with the present invention;
FIG. 4(a) shows a block circuit diagram of the inner portion of a
controller used in the knock detecting apparatus in accordance with one
embodiment of this invention which is employed in the apparatus of FIG. 3;
FIG. 4(b) shows a block schematic diagram of the construction of a knock
signal pickup;
FIG. 4(c) shows a time chart illustrating the operation of the knock signal
sensor;
FIG. 5 shows a flow chart of a signal processing operation for judging the
occurrence of knocking in the embodiment of FIG. 3;
FIG. 6 is a flow chart showing a signal processing operation for judging
the occurrence of knocking in the embodiment of FIG. 3;
FIGS. 7(a) and 7(b) show block schematic diagrams of another controller and
another signal pickup respectively which may be used in the present
invention;
FIG. 8 is a time chart illustrating a signal pickup operation in the
embodiment of FIGS. 7(a) and 7(b);
FIG. 9 is a flow chart showing a knocking judging operation in the
embodiment of FIGS. 7(a) and 7(b);
FIG. 10 shows a block diagram of an internal combustion engine to which a
knock detecting apparatus in accordance with another embodiment of the
present invention is applied;
FIGS. 11(a) and 11(b) show an explanatory representation of a resonance
vibration mode;
FIG. 12 shows a currently preferred embodiment of a portion of the knock
detection apparatus used in the embodiment of FIG. 10;
FIGS. 13(a)-(h) show waveforms useful in explaining the operation of the
apparatus of FIG. 10;
FIGS. 14(a)-(e) show flowcharts of knock detection procedures in the
embodiment of FIG. 10;
FIG. 15 shows a graphical representation of the frequency characteristics
used for knock detection; and
FIG. 16 shows a graphical representation of the change of frequencies for
knock detection when subjected to aged deterioration of the engine.
In the Figures like reference numerals denote like parts.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Before describing the embodiments, the facts, which the inventors of the
present invention have ascertained, regarding the relationship, which
constitutes the basis of the present invention, between an output signal
from a knock detecting vibration sensor, and a crank angle at which the
pickup of the output signal is started will be illustrated with reference
to FIGS. 1(a) and 1(b) of the accompanying drawings.
FIG. 1(a) shows an output signal from an engine vibration detecting sensor,
and a range of crank angles .theta..sub.1 (starting from 10.degree. after
TDC) at which the pickup of the output signal is started and a range of
other crank angles .theta..sub.2 (starting from 16.degree. after TDC) to
which .theta..sub.1 is to be changed, where TDC denotes top dead center
and ATDC denotes after top dead center. For the benefit of explanation the
range of crank angles, that is time or arcuate length of angle
.theta..sub.1 and .theta..sub.2 are the same, their starting position only
being varied. However, this invention contemplates both the starting point
of .theta..sub.1 and .theta..sub.2 being different from one another and
the time or angles .theta..sub.1 and .theta..sub.2 being different from
one from one another. The results of a frequency analysis carried out with
respect to each of these crank angles are shown as m(.theta..sub.1),
m(.theta..sub.2) in FIG. 1(b). As is clear from these Figures, the
characteristic frequency of knocking fluctuates when the commencement
point of detection for a range of crank angles is varied (even when
.theta..sub.1 equals .theta..sub.2). It is considered that the cause of
this phenomenon resides in the fluctuation of natural frequency of
knocking which is due to the variation of temperature in a cylinder in an
expansion stroke. Therefore, in order to judge the occurrence of knocking
with reference to a vibration component at a specific frequency, a signal
is picked up in the range of crank angles in which the characteristics of
knocking most distinctly appear with respect to the frequency, and hence
knock detecting accuracy is improved.
A method of predetermining the range of crank angles at which the pickup of
signal is carried out with respect to each frequency will now be described
with reference to FIG. 2.
FIG. 2(a) shows the output from a vibration sensor and FIG. 2(b) shows the
range of crank angles .theta..sub.1, .theta..sub.2 . . . .theta..sub.n at
which the vibration sensor output is detected (picked up).
FIGS. 2(c) and 2(d) show the results of determination of spectral levels of
different frequencies f.sub.1, f.sub.2, f.sub.3 in a frequency analysis
carried out with the crank angle, in which the vibration sensor output
signal is changed in the FIGS. 2(c) and 2(d) respectively. In FIG. 2(c)
the spectral level of frequency corresponds to a case where knocking is
not detected and in FIG. 2(d) the spectral level of frequency corresponds
to a case where knocking occurs and both graphs are plotted
correspondingly to the crank angles in the middle of the ranges of crank
angles in which the frequency analysis is carried out. Since the time of
occurrence of knocking fluctuates slightly in every ignition stroke, these
spectral levels are determined by averaging spectral levels corresponding
to a predetermined number of ignition strokes (for example, 50 ignition
strokes). FIG. 2(e) shows a ratio of spectral level in a case where
knocking occurs to that in a case where knocking is not detected, that is
a S/N ratio determined with respect to each frequency and correspondingly
to each crank angle range on the basis of what is shown in FIGS. 2(c) and
2(d) whereby the crank angle ranges for f.sub.1, f.sub.2, f.sub.3 may
differ from one another.
The range of crank angles in which the pickup of a signal is carried out is
set on the basis of what is shown in FIG. 2(e) to a range in which the S/N
ratio with respect to each frequency becomes not lower than a
predetermined level (for example, not less than 1.5).
As shown in FIG. 2(f) this procedure enables the determination of a crank
angle .alpha..sub.fi (where i relates to frequency 1, 2 . . . ) at which
the pickup of a signal is started, and the range .beta..sub.fi (i=1, 2 . .
. ) of crank angles corresponding to the time between the starting of
pickup of signal and the ending thereof (these times being the same or
different from one another).
FIG. 3 shows an embodiment of system configuration of a control apparatus
for an internal combustion engine. Air enters the inlet of an air cleaner
1, and is sucked into a cylinder of an engine 7 through a duct 3,
containing a throttle body 5 having a throttle valve, and a suction pipe
6. The flow rate of the inlet air is detected, for example, by a hot wire
type air flow sensor 2 provided in the duct 3, and a signal representative
of the flow rate detected is inputted to an engine control unit (ECU) 9.
Fuel injected from an injector 16 is mixed with the sucked air, and the
resultant gaseous mixture is supplied into the cylinder of the engine 7. A
high voltage generated in an ignition coil 13 is distributed by a
distributor 14 to an ignition spark plug 15 of each cylinder of the
engine. The gaseous mixture sucked into the cylinder is then compressed in
the engine 7, ignited by the ignition spark plug 15 and thereafter
discharged from an exhaust pipe 8. The exhaust pipe 8 may be provided with
an exhaust gas sensor 11 (for example, an oxygen (O.sub.2) sensor), an
output signal from which is also inputted to the control unit 9.
The rotational condition of the engine is detected by a crankshaft 4 POS
crank angle sensor 18, from which a POS signal (crank angle position
signal) and a crank angle reference sensor 19 from which a REF signal is
outputted indicative of a crank angle reference position. A vibration
detecting sensor 17 is attached to the engine 7, and an output signal
therefrom is also inputted into the control unit 9. The control unit 9 is
adapted to compute the fuel feed rate and ignition time on the basis of
the signals from the foregoing and various other sensors (such as water
temperature) and to output a control signal to each actuator of the
engine.
FIG. 4(a) shows the construction of part of the engine control unit 9. In
this respect, the control unit 9 consists of a CPU 20, an A/D converter
21, a ROM 22, an input I/O 23, RAM 24 and an output I/O 25. The REF signal
and the POS signal detected by the crank angle sensor 12 are inputted into
the CPU 20 through the input I/O 23. An output signal from the vibration
sensor 17 is inputted into the CPU 20 through the A/D converter 21. The
CPU 20 is adapted to carry out computation in accordance with a program
held in the ROM 22, and the result of the computation is outputted as an
ignition timing signal .theta..sub.ign from the output I/O 25 to the
relevant actuator. The crank angle at which the pickup of a signal from
the vibration sensor is started and the range of crank angles are set to
optimum levels by the above-described procedure and stored in the ROM 22,
and the retention of necessary data during the computation is performed by
the RAM 24.
The operation of picking up a signal from the vibration sensor will now be
described with reference to the construction of the pickup shown in FIG.
4(b) and the time chart shown in FIG. 4(c). Referring to FIG. 4(b), a
counter 30 is for use in determining the crank angle based on the rising
part of the REF signal, counter 3 is for use in determining the variation
of crank angle during the time after starting the pickup of the signal,
compare register 32 is adapted to set an angle .theta..sub.fi at which the
pickup of the signal is started, and compare register 33 is for use in
setting the range .beta..sub.fi of crank angles corresponding to the time
of pickup of signal (values on these compare registers 32, 33 are set by
the CPU 20) . Comparator 34 is adapted to check an actual crank angle as
to whether it agrees with a predetermined value X, and comparator 35 is
adapted to check the variation of crank angle during the time between the
starting and ending of pickup of a signal as to whether the level of the
variation agrees with another predetermined value Y. When the agreement
mentioned above is ascertained in the comparators 34, 35, trigger signals
for ordering the starting and ending of A/D conversion are outputted
therefrom to the A/D converter 21. An A/D converted signal is inputted
into the CPU 20. In this embodiment, the number set by the counters,
compare registers, comparators and A/D converters correspond to the
frequency to be detected.
Referring to the time chart of FIG. 4(c), the procedure for carrying out a
signal pickup operation will be described. The counter 30 is adapted to
count the POS signal from the time of initiation of the REF signal. The
crank angle .alpha..sub.fi at which the pickup of the vibration sensor
signal is started is set by the number of POS signals starting from
initiation by the signal reaching the predetermined value X required by
the compare register 32. Thus, when the value in the counter 30 agrees
with the predetermined value X required by compare register 32, an output
signal from the comparator 34 rises, and the A/D conversion is started.
The counter 31 is adapted to count the POS signals from the time at which
the output signal from the comparator 34 rises. The range .beta..sub.fi of
crank angles corresponding to the time during which the vibration sensor
signal is picked up is set as the number of POS signals starting from the
time of beginning of A/D conversion in the compare register 33. When the
value in the counter 31 reaches the value Y, an output signal from the
comparator 35 rises, and the A/D conversion ends. These actions are
performed for each of the different detected frequencies.
The computation made by the CPU 20 for determining the occurrence or
non-occurrence of knocking will now be described with reference to the
flow chart of FIG. 5.
First, in a step 500, the values of crank angles .alpha..sub.fl
-.alpha..sub.fn at which the pickup of signals is started and the ranges
.beta..sub.fl -.beta..sub.fn of crank angles in which the pickup of
signals is carried out, with respect to the detected frequencies f.sub.l
-f.sub.n of the output signals from the vibration sensor, which are read
and set in the compare registers X.sub.l -X.sub.n, Y.sub.l -Y.sub.n are
preset in accordance with the above-described procedure.
In a step 501, a signal is picked up in accordance with the above described
procedure within the range of crank angles set in the step 500 with
respect to each detected frequency. The pickup of a signal referred to
above is performed in a predetermined sampling cycle (for example, every
12.mu. sec).
In a step 502, the data received with respect to each detected frequency is
subjected to a frequency analysis to determine the magnitude m.sub.fl
-m.sub.fn of a vibration component. FFT. (Fast Fourier Transform) or WFT
(Walsh to Fourier Transform described by Nobuo Kurihara on pp. 38-44,
"Keisokujido-gakkai Ronbunshu 18, No. 10 (October 1982)"), both known per
se, may be used as a frequency analysis method.
In a step 503, m.sub.fl -m.sub.fn determined in the step 502 and
predetermined levels l.sub.fa -l.sub.fn set beforehand with respect to
each detected frequency are compared with each other, and, for example,
when any one of the m.sub.fl -m.sub.fn is larger than the predetermined
levels l.sub.fl -l.sub.fn, a decision that knocking occurs is given. When
a decision that knocking occurs is given, the ignition is retarded with
respect to normal ignition time in a step 504.
Another embodiment of the present invention will now be described. In this
embodiment, the invention is applied to a knocking apparatus in which the
frequency to be detected is changed in accordance with the operational
condition of the engine, which is represented by the number of revolutions
per minute thereof, so as to improve the signal detecting accuracy.
Although the construction of the apparatus in this embodiment is identical
with that of the apparatus in the above-described embodiment, the knocking
detecting procedure in the former is different from that in the latter.
A frequency to be detected is changed in dependence upon the number of
revolutions per minute of the engine with reference to the following Table
1, and the range of crank angles in which the pickup of a signal is
carried out is changed in dependence upon the changed frequency to be
detected.
TABLE 1
______________________________________
Number of Crank angle Range of
revolutions at which the
crank angles
per minute pickup of in which the
of engine
Frequency to
signal is pickup of signal
(rpm) be detected started is carried out
______________________________________
1000-2000
f.sub.1 .alpha..sub.f1
.beta..sub.f1
2000-3000
f.sub.2 .alpha..sub.f2
.beta..sub.f2
3000-5000
f.sub.3 .alpha..sub.f3
.beta..sub.f3
______________________________________
The computation carried out in the CPU 20 for judging whether knocking
occurs or not will be described with reference to the flow chart in FIG.
6.
In a step 600 in this flow chart, one of the predetermined frequencies to
be detected is selected in accordance with the number of revolutions per
minute of the engine. In a step 601, a crank angle o at which the pickup
of a signal is started and the range of crank angles .beta. in which the
pickup of signal is carried out are set in a register, both .alpha. and
.beta. being pre-set for the particular frequency to be detected which was
selected in the step 600. In a step 603, a frequency analysis with respect
to the frequency to be detected set in the step 602 is carried out by FFT
or WFT to determine the magnitude m of a vibration component. In a step
604, m is compared with a predetermined level l, and, when the former is
higher than the latter, a decision that knocking occurs in given. When a
decision that knocking occurs is given, the ignition is retarded in a step
605.
Yet another embodiment of the present invention will now be described. The
system configuration of this embodiment is identical with that of the
embodiment of FIG. 3. The construction of a control unit 9 in the third
embodiment is shown in FIGS. 7(a), 7(b). In FIG. 7(a), a band-pass filter
40 is provided for separating a vibration component of characteristic
frequency of knocking from an output signal from the vibration sensor (not
shown) and an integrator 41 is provided for carrying out integration of
the output signal from the band-pass filter 40 within a predetermined
range of crank angles. The number of each of the band-pass filters 40,
integrators 41 and A/D converters 21 corresponds to the number of specific
frequencies to be detected.
An operation of picking up a signal from a vibration sensor will be
described with reference to the construction of hardware shown in FIG.
7(b) and the timing chart of FIG. 8. Referring to FIG. 7(b), the counter
30 determines a crank angle based on the rising edge of the REF signal,
counter 31 determines the variation of crank angle occurring after the
starting of the pickup of signal, compare register 32 sets the angle
.alpha..sub.fl in which the pickup of signal is carried out. The values in
the compare register 32 is X and in the register 33 is Y, both values
being set by CPU 20. Comparator 34 is for checking an actual crank angle
as to whether the value thereof agrees with that in the compare register
32, and comparator 35 is for checking the variation of crank angle whether
the value thereof agrees with that in the compare register 33.
Referring to the time chart of FIG. 8, the rising of a POS signal is
counted in the counter 30 to determine the actual crank angle. When the
value of the crank angle obtained agrees with the value X in the compare
register 32, an output signal from the comparator 34 rises, and an
integration operation of the integrator 41 for a vibration component of an
output from the vibration sensor is started, the vibration component being
obtained through the band-pass filter 40. When the value in the counter 31
agrees with the value Y in the compare register 33, an output signal from
the comparator 35 rises, and an output signal from the integrator is then
subjected to A/D conversion. These operations are carried out with respect
to the vibration component of each frequency. The above operations enable
the determination of the level of the vibration component in the preset
range of crank angles.
The computation mentioned above and carried out in the CPU 20 for judging
whether knocking occurs or not will now be described with reference to the
flow chart in FIG. 9.
Firstly, in a step 900, crank angles .alpha..sub.fl -.alpha..sub.fn at
which the integration of each detected frequency is started and ranges
.beta..sub.fl -.beta..sub.fn of crank angles in which such integration is
carried out are read and set in compare registers X.sub.l -X.sub.n,
Y.sub.l -Y.sub.n. These values are set beforehand as described above.
In the integrator in the control unit 9, the integration of each detected
frequency is carried out within the range of crank angles set in the step
900. In a step 901, the results S.sub.fl -S.sub.fn of integration of
detected frequencies f.sub.l -f.sub.n are read.
In a step 902, S.sub.fl -S.sub.fn are compared with levels l.sub.fl
-l.sub.fn pre-set with respect to the detected frequencies, and, when
S.sub.fi >l.sub.fi with respect to a predetermined frequency, for example,
f.sub.i wherein i=1-n, a decision that knocking occurs is given. When a
decision that knocking occurs is given in this step, the ignition time is
delayed in a step 903.
As mentioned above, a decision of occurrence of knocking is given in this
embodiment by using the results of integration of a vibration component in
the range of crank angles, in which the characteristics of knocking appear
most distinctly with respect to each detected frequency. Accordingly, the
knocking detecting accuracy is improved.
In this embodiment, a decision of occurrence of knocking is given by using
a plurality of frequencies to be detected. Beside these techniques, the
techniques for changing the frequency to be detected, in accordance with a
change in the operational condition of the engine and changing the range
of crank angles in which integration is carried out in accordance with the
resultant frequency to be detected, may also be used.
Another embodiment of this invention will now be described with reference
to FIG. 10
The internal combustion engine shown in FIG. 10 is applied with the knock
detection apparatus of this invention and is similar to the embodiment
shown in FIG. 3 except that there are also shown various sensors such as a
speed sensor 121, a water temperature sensor 106, and a throttle valve
opening sensor 105. The signals from the various sensors are analysed to
determine an appropriate fuel injection quantity and ignition timing for
the operation of the engine. Thus, the result of analysis is output from
the I/O device 23 to operate the fuel injector 16 and the ignition coil
13.
The water temperature sensor 106 measures the temperature Tw of the cooling
water for the engine, and the result is used to compensate the control of
the engine.
The CPU 20 divides intake air flow by the number of engine revolutions and
adds to the result a correction factor determined by, for example, water
temperature, in order to calculate injection quantity.
The fundamental value of ignition timing is specified by injection quantity
and the number of engine revolutions and is corrected according to the
conditions of water temperature and the number of engine revolutions.
The knock sensor 17 is mounted on the cylinder block of the engine to
detect vibration on the occurrence of knock and to convert the vibration
signal into an electrical signal representative of the vibration.
The knock sensor may alternatively be a cylinder internal pressure sensor
117 attached to the combustion chamber between the spark plug 15 and the
engine to detect a change in the pressure inside the cylinder and convert
the pressure into a knock representative signal.
The engine control unit 9 has a timer 102 provided for obtaining the total
operating time of the engine. A wheel of the automobile is provided with
the speed sensor 121 so that a speed signal VSP from the speed sensor 121
can be counted by a counter 103 in the engine control unit 9 to obtain the
total distance that the automobile has covered.
The total operating time and the total distance are held in a non-volatile
ROM (not separately shown) and a built-in backup battery 107 is provided
so that the engine control unit 9 is able to retain engine and vehicle
data when the main battery (not shown) power is cut off.
Knocking detection with this embodiment will now be described.
Let the mode with respect to the diameter of a cylinder of the engine 7 be
n and for the mode with respect to the circumference of the engine
cylinder be m. Then, the vibration of the engine during combustion has a
frequency .rho.nm and a corresponding resonance frequency fnm. As an
example, an engine used in test gave the values of vibration frequency and
resonance frequency shown in FIG. 11(a).
The knock sensor 17 mounted to the cylinder block of the engine is now
assumed to have a frequency characteristic including all the
above-mentioned frequencies particular to the occurrence of knock and also
to be uniformly sensitive to them.
Analysing a knocking signal gives a distribution such as that shown in FIG.
11(b).
Therefore, if the frequency characteristic of the sensor is known in
advance to be not flat, the frequency characteristic can be made to be
flat by providing the head amplifier, described later herein, with a
characteristic which is the inverse of the known frequency characteristic.
Now, the processing of knocking signals will be described with reference to
FIG. 12.
A knock signal s is amplified by a head amplifier 120. As stated above, the
frequency characteristic of the sensor output is changed inversely by an
equalizer 121, and is filtered by low pass filter 122 and amplified by a
variable amplifier 123 to be within the voltage input range of an A/D
converter 124. The amount of the amplification by the variable amplifier
123 is alterable in accordance with the level of an input signal or the
number of engine revolutions in response to instructions from the I/O
device 23. However, the amount of amplification is constant in the knock
detecting period for knocking signal frequency analysis.
The knock detecting sampling period 2.sup.n for knocking signal frequency
analysis, operates at a predetermined angle (time) .theta.open (FIG.
13(c)), at which knock tends to occur, after the top dead centre point.
This angle .theta.open can be found by specifying the leading edge of the
reference signal REF (FIG. 13(b)) as zero and by counting the position
signal POS (FIG. 13(a)) as shown in FIG. 13(c).
When the result of the counting coincides with the angle .theta.open the
CPU is enabled for an A/D conversion termination interruption, FIG. 13(d),
thereby starting the processing by the A/D converter 124 shown in FIG. 12.
This A/D conversion is, as shown in FIG. 13(d), performed at predetermined
data cycles each having period .tau.. When the A/D conversion terminates,
an interrupt occurs to the microcomputer, and, during the A/D conversion
termination interruption, converted signals are sequentially sent to the
RAM 13.
Here, the cycle .tau. of this A/D conversion has been specified in advance
so that its inverse can be a frequency twice or more times as high as the
highest of the frequencies to be analysed.
The low pass filter 122 provides sufficient damping for the frequency fcut
which is higher than 1/(2.tau.).
When the number of data resulting from the A/D conversion amounts to, for
instance 2.sup.n at the time to, shown in FIG. 13(f), the A/D conversion
termination interrupt ends. At this time to a frequency analysis flag
comes ON and frequency analysis starts.
The frequency analysis is performed by taking sampling data (block A) from
RAM 24 and conducting highspeed Fourier transformation 125 and butterfly
calculation (for this method, see text book "FFT Katsuyo Manyuaru," by
Kito, Nippon Noritsu Kyokai, Oct. 30, 1985) to obtain data B totalling
2.sup.n representative of amplitude of the different sampling frequencies
each from sampling data A totalling 2.sup.n.
Then, from these 2.sup.n frequencies, spectrum portions So to Sk
corresponding to frequencies f.sub.o to f.sub.k totalling k (k>1), which
are predetermined by experimentation, are obtained as data S.sub.o to
S.sub.k in block C. The data C are tone quality indexes in accordance with
knock.
The spectrum portions S.sub.o to S.sub.k are multiplied by weighting
quantities W.sub.l to W.sub.k in block 126 so as to obtain the knocking
signal strength I.
At comparator 127, the signal strength I is compared with a reference
strength I.sub.0 which is a strength wt the time that no knock occurs,
and, when the former is greater than the latter, it is decided that knock
has occurred.
When this decision is made, a knock occurrence flag is set as shown in FIG.
13(g), and ignition timing is delayed by a predetermined angle .theta.ref
(FIG. 13(h)), and then the timing is gradually recovered by, for example,
+1.degree. steps after a specified interval Tadv, as in the known method
of ignition timing control.
Now, a microcomputer processing needed for the above operation will be
described with reference to FIGS. 14(a) to (e).
Firstly, the process shown in FIG. 14(a) is performed in response to the
leading edge of the reference signal to identify a cylinder, and
predetermined angle .theta.open is provided.
During the above process, when the angle .theta.open is found by counting
position signals, an angle interrupt is caused so as to start the process
shown in FIG. (14b). During the angle interrupt, the CPU is enabled for an
A/D conversion termination interruption, and a sampling counter is
initialized to all zeros with a sampling data store pointer being set to
the leading address in the store area.
This A/D conversion termination interruption starts the process shown in
FIG. 14(c). During this process, the result of the A/D conversion is
entered into the address pointed to by the sampling data store pointer to
increment the pointer and the sampling counter (at steps 1400). When the
sampling counter reaches 2.sup.n, the A/D conversion termination
interruption ends, and a frequency analysis flag comes ON (at step 1401).
On the other hand, the process shown in FIG. 14(d) is provided as a timer
task activated in a predetermined cycle. During this process, a frequency
analysis flag is checked, and, when a frequency analysis flag comes ON, a
high-speed Fourier transformation subroutine is activated (at step 1402).
After the high-speed Fourier transformation is completed, the process at
step 1403 is performed for obtaining spectrum portions S.sub.l to S.sub.k
corresponding to frequencies f.sub.l to f.sub.k.
Now, frequencies particular to the occurrence of knock change slightly
because of the number of engine revolutions and the timing of ignition and
also vary with other factors such as the position of the piston on the
occurrence of knock, so with the value of the spectrum portions S.sub.l to
S.sub.k as they are it is impossible to accurately decide the occurrence
of knock.
In this embodiment, therefore, as shown in FIG. 15 peaks are obtained among
the spectrum portions within the range corresponding to .DELTA.f.sub.l to
.DELTA.f.sub.k around the particular frequencies made up of the
frequencies f.sub.l to f.sub.k, and the peaks are used instead of the
particular frequencies made up of the frequencies f.sub.l to f.sub.k.
Note that the average of the samples within each spectrum portion within
the range corresponding to .DELTA.f around the particular frequencies may
alternatively be used.
Also note that the peak frequency within a spectrum portion .DELTA.f may be
used as the central frequency for the next ignition operation.
The spectrum portions S.sub.l to S.sub.k obtained in the above-mentioned
way are multiplied by weighting coefficients W.sub.l to W.sub.k which
decrease when the S/N ratio increases in order to obtain the knocking
intensity I (at step 1404), and this intensity I is compared with the
reference intensity I.sub.o at step 1405.
When the knocking intensity is greater than the reference intensity, a
knock occurrence flag comes ON (step 1406).
FIG. 14(e) illustrates the calculation for ignition timing. When a knock
occurrence flag comes ON as described above, ignition timing is delayed by
the angle .theta.ref, and an ignition timing retention timer is set to the
interval Tadv (step 1407).
The interval Tadv is subtracted from each time the cycle for the timer task
is completed. When the interval Tadv reaches zero, the angle .theta.ref is
subtracted from once. Unless the angle .theta.ref becomes zero as a
result, the interval Tadv is set again. In the course of this operation,
ignition timing is delayed every time knock occurs with the result that
knock control can be implemented (step 1408).
Now, the particular frequencies f.sub.l to f.sub.k for the detection of
knock are, as shown in FIG. 16, subject to the aged deterioration of the
engine.
In view of this fact, as described with reference to FIG. 10, this
embodiment has therein the timer 102 and speed sensor 121 to obtain the
total operating time of the engine and the total distance that the
automobile has covered. By virtue of the built-in battery 107, the total
operating time and the total distance covered are retained even when the
engine control unit 9 has the power thereto cut off.
By measuring the total operating time and total distance, the particular
frequencies f.sub.l to f.sub.k for the detection of knock are modified in
such a way as to compensate for such an aged deterioration which has the
characteristics shown in FIG. 16 thereby determining the detection of
knock with higher precision.
Although in this embodiment, again high-speed Fourier transformation has
been used to analyse frequencies, another frequency analysis method such
as WHT transformation known per se may alternatively be employed. The WHT
transformation allows obtaining the particular frequencies f.sub.l to
f.sub.k without using 2.sup.n spectra and thus shortening calculation
time.
Yet another frequency analysis may be used, for instance, a method of using
a digital bandpass filter for predetermined frequencies f.sub.l to f.sub.k
and thereby slightly altering each coefficient in Z transform to alter the
central frequency in the bandpass width.
As will now be evident from the above, in the present invention the range
of crank angles in which a signal is picked up is changed in accordance
with the frequency to be detected so that the occurrence and
non-occurrence of knocking can be judged in a range of crank angles in
which a vibration component of the frequency in use appears most
characteristically. Accordingly, the window in which knock detection is
effected is adjustable in position and length so the knocking detecting
accuracy can be improved, and the utilisation of these techniques enables
the ignition timing to be more accurately controlled in dependence upon
the occurrence of knocking. Therefore, the engine output power and fuel
consumption can be improved.
The central frequency on the occurrence of knock also changes with the
temperature of the cooling water, the temperature and humidity of intake
air and operating conditions. Therefore, altering the central frequency in
dependence upon these conditions allows knock detecting with yet higher
precision.
By the present invention, the occurrence of knock can always be decided
with high precision by checking frequencies particular to the occurrence
of knock in harmony with the operating conditions of the engine so as to
achieve accurate knock control.
In addition, selection of more than one frequency allows using appropriate
frequencies to detect knock even when the engine operates with high load
and at high speed. Also the difference in the proportion of the knocking
intensity I to the reference intensity I.sub.o is large enough between the
state of having knock occur and the state of having no knock, which leads
to accurate decision about the occurrence of knock.
Furthermore, since knock control is operable even when the engine operates
with high load and at high speed, the operating point for the engine can
be brought closer to the ignition time required for the MBT control,
leading to increase in engine output and decrease in fuel consumption
rate.
It is to be understood that the invention has been described with reference
to exemplary embodiments, and modifications may be made without departing
from the spirit and scope of the invention as defined in the appended
claims.
Top